A Light-Emitting Diode (LED), as used herein, is a semiconductor light source for generating a light at a specified wavelength or a range of wavelengths. LEDs are traditionally used for indicator lamps, and are increasingly used for displays. An LED emits light when a voltage is applied across a p-n junction formed by oppositely doping semiconductor compound layers. Different wavelengths of light can be generated using different materials by varying the bandgaps of the semiconductor layers and by fabricating an active layer within the p-n junction. Additionally, an optional phosphor material changes the properties of light generated by the LED.
Traditionally, LEDs are made by growing a plurality of light-emitting structures on a growth substrate. The light-emitting structures along with the underlying growth substrate are separated into individual LED dies. At some point before or after the separation, electrodes or conductive pads are added to the each of the LED dies to allow the conduction of electricity across the structure. The light-emitting structure and the wafer on which the light-emitting structure is formed is referred to herein as an epi wafer. LED dies are then packaged by adding a package substrate, optional phosphor material, and optics such as lens and reflectors to become an optical emitter.
The LED die is electrically connected to circuitry on the package substrate in a number of ways. One conventional connection method involves attaching the growth substrate portion of the die to the package substrate, and forming electrode pads that are connected to the p-type semiconductor layer and the n-type semiconductor layer in the light-emitting structure on the die, and then bond wiring from the electrode pads to contact pads on the package substrate. When wire bonds are used at both the p-contacts and n-contacts, light may escape from the sides of the LEDs, which is generally undesirable. Also, wire bonding uses space within the package footprint, and this space is generally viewed as wasted. Thus, wire bonding approaches in one aspect can be inefficient.
Another conventional connection method involves inverting the LED die and using solder bumps to connect the electrode pads on the light-emitting structure directly to the package substrate, commonly referred to as a flip chip. However, flip chip processes at this level of LED manufacturing can be costly and inconvenient to implement. Yet another conventional connection method involves using hybrid connectors. One semiconductor layer, for example the p-type layer, may be wired bonded to the package substrate while the other layer (n-type layer) may be soldered to the package substrate.
Therefore, while existing methods of manufacturing the LED devices have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.